S-L-O-W underwater drifter

[bunk]

Hi
Ok, I'm working on an art project here... imagine an old galvanised tank, maybe 2' x 3' x 3'deep. It's in a room which is quite dark. As you peer into the tank, you see that it is full of water and in the bottom there are tiny lights which look like city lights from a great height. But as you look, there is a movement, a darkness moving between you and the lights, difficult to make out and moving very slowly... I need to make one of those!
Spec: neutrally buoyant, movement maybe around 1-2 cm (0.5-1") per second, battery-powered, autonomous, stupid, relies on shape to get it out of corners (or I might use transparent curves inside tank to stop it getting stuck).
I've read the threads on underwater propulsion and muscle wire and looked at robotic fish stuff, but this really needs to be simple! And cheap! I've taken apart a wind-up toy fish with a waggy tail, and have a battery-powered submarine motor which is WAY too powerful! I have a vision of something which does a little wag or flap (like a ray?!) maybe every 10 sec or so... but I have no idea how to make something that does that...
Any ideas would be greatly appreciated...

[Asellith]

make your neutral bouyancy object and then place a small prop at both ends of the tank. Then have the props randomly run at intervals. Like pulse the left one for 4 seconds then the left one for 3 seconds and then change the durations and repeat. The object will move around in the current and randomly move around the tank without electronics or need of batteries. So you could power the props off the same source that is running the lights.

[airman00]

there are toys to do what you want

http://www.toysplash.com/productinfo.aspx?productid=151387&engine=pricegrabber

called swim ways

[bunk]

Asellith and airman00 - many thanks for your thoughts! I like the idea of making currents and letting the thing ride those - and those toys look good if I could get one to move slowly enough... hmm I'll keep thinking about it...

[Admin]

You want really slow and simple?

Put soap on one end of it. Serious.

http://pbskids.org/zoom/activities/phenom/soappoweredboat.html

[bunk]

Hi Admin
My drifter needs to be underwater, otherwise I'd try the soap trick! Thanks anyway, though!

I bought a battery-operated fish to hack, but the gears are SO noisy! (haven't tried it underwater yet - maybe that will be quieter). Is there a simple circuit which I can make which would operate the motor in the fish intermittently? I think I'd be pretty much there then - if I could add a timer which made the motor come on for say a second every 10 or 20 seconds... but I just don't know where to start... I've just spent around 2 hours searching the web... if anyone could give me a quick tutorial, I'd be very grateful! (it's just a standard electric toy motor which runs off 2 AA batteries). Also, if anyone knows what size resistor to slow motors this small, that would be really useful to know too...

Thanks!! Bunk

[Admin]

My drifter needs to be underwater, otherwise I'd try the soap trick!

it works underwater, too

I bought a battery-operated fish to hack, but the gears are SO noisy! (haven't tried it underwater yet - maybe that will be quieter).

yea, water really dampens sound. My robot fish is really quite underwater . . .


Try out pager motors, they are quite and weak (for going slow).

[bunk]

Oh! OK. I thought the soap trick needed surface tension to work... I'll give it a go, thanks

Is a pager motor like the tiny motor which makes mobile phones vibrate? People just don't seem to use pagers here in the UK...

Thanks for your comments, Admin!

[Admin]

Is a pager motor like the tiny motor which makes mobile phones vibrate? People just don't seem to use pagers here in the UK...

yeap

try here:
http://www.solarbotics.com/motors_accessories/

but I'm sure you can find one cheaper if you look/ask around


edit: forgot to mention, you can buy an el-cheapo remote control toy from walmart or radioshack and hack out the remote control electronics.

[Asellith]

Let me do some research we actually found a chip that is used in those cheap RC cars for control. They use OOK I think or the one we found did. very simple would have done most of what we needed for the project I was working on but it was found two late.

[SixRingz]

Ok, call me retarded for posting this on a robot forum, but how about using gods own underwater neutrally boyant biological robots: Fish.
This is of course if you want to get this done easiest possible for an exhibition or something.